1. Field of the Invention
The present invention relates to an innercam system, distributor-type fuel injection pump used for supplying fuel to engines, i.e., to a fuel injection pump which adopts a method whereby plungers are caused to make reciprocal movement in the direction of the radius of a rotor that rotates in synchronization with the engine.
2. Description of the Related Art
Innercam system, distributor-type fuel injection pumps of this type in the known art include the pump disclosed in Japanese Unexamined Patent Publication No. S59-110835. In this pump, an innercam ring 1 is provided concentrically around a fuel distribution rotor 4 (rotor) inside a fuel chamber 121 (chamber). Force feed plungers 21 and 22 are provided on the cam surfaces formed on the inside of the innercam ring 1 via rolling bodies 23 and 24 (rollers) and shoes 25 and 26 and these force feed plungers 21 and 22 are caused to make reciprocal movement in the direction of the radius of the fuel distribution rotor 4. A pump chamber 2 (compression space) whose volumetric capacity changes with the movement of the force feed plungers 21 and 22, intake ports 51-54 for taking in fuel to the pump chamber 2 during the intake process, a distribution port 6 for delivering fuel that has been pressurized in the pump chamber 2 during the force feed process, and overflow ports 71-74 for cutting off delivery of fuel are formed at the fuel distribution rotor 4. A ring-shaped member 7 (control sleeve) is externally fitted on the rotor with a high degree of oil tightness, covering the overflow ports 71-74 and by adjusting the position of this ring-shaped member 7 in the direction of the axis, the cutoff timing (the timing with which the compressed fuel flows out to the fuel chamber 121) during the force feed process is changed, thereby changing the fuel injection quantity.
As a result of a great deal of research performed on innercam system, distributor-type fuel injection pumps of this type, the inventor of the present invention has learned that if intake ports and cutoff ports are made to open into the area where the pressure is somewhat higher than the pressure around the rollers and shoes, fuel intake into the compression space is facilitated due to the pressure difference between the ends of the plungers. The plungers can be made to move toward the outside due to this pressure difference and, at the same time, the rollers and the like can be cooled with the fuel in the low pressure fuel area. As a result, the inventor of the present invention and others have thought of partitioning the area on the upstream side of the feed pump, which includes the area surrounding the rollers, from the area on the downstream side of the feed pump, which communicates with the inflow/outflow ports of the rotor. This idea has resulted in the development of, for instance, the distributor-type fuel injection pump shown in FIG. 10.
In this distributor-type fuel injection pump, with a rotor support member 7 and an adaptor 9 which are secured inside a housing 2, the area surrounding the port 31, which takes in and cuts off fuel, is separated from the area where the rollers 25 and shoes 24 are provided, and by inserting a rotor 16 through the rotor support member 7 and the adaptor 9 with a high degree of oil tightness and in such a manner that it can rotate freely, pressure in the area surrounding the port 31 is maintained higher than the pressure around the rollers and the like. Note that in the figure, reference number 3 indicates a drive shaft for rotating and driving the rotor 16 and a feed pump 4. Reference number 26 indicates a cam ring for regulating the movement of the plungers 22 via the rollers 25 and the shoes 24. Reference number 33 indicates a distribution port for supplying fuel that has been compressed in a compression space 23 to a distribution passage 32. Reference number 34 is a control sleeve for adjusting the injection quantity and reference number 49 indicates a fuel inflow port for supplying fuel to the area where the rollers 25 and the like are provided.
However, in the injection pump structured as described above, it has been verified that the portion where the rotor 16 is in sliding contact with its support member tends to seize. This phenomenon is observed particularly in the area where the front end of the rotor 17 slides in contact, rather than at the base end (the portion where the rotor slides in contact with the rotor support member 7 in the distributor-type fuel injection pump shown in FIG. 10) and such seizure may occur even if that area is coated.
We are still looking into the specific causes of this, but we anticipate that when, for one reason or another, a rotational misalignment occurs in the rotor, the amount of heat generated in the area where it is in sliding contact, increases during high speed rotation. This reduces the viscosity of the fuel used for lubricating this sliding contact area, resulting in oil film loss, which, in turn, causes seizure. In addition, due to the high pressure fuel supplied to the distribution port, the surface of the rotor that comes in contact with the rotor support member at 180.degree. from the distribution port will be under a high surface pressure. This may be calculated as (fuel pressure X opening area of the distribution port) and since this surface pressure increases when the discharge pressure is increased, this is also a possible cause of seizure between the rotor and the barrel.